This is an uncontrolled, open-label, Phase III trial of peginterferon alfa-2a (Pegasys) in participants coinfected with human immunodeficiency virus (HIV) and hepatitis C virus (HCV). Participants with HIV/HCV who do not show negative or reduced HCV ribonucleic acid (RNA) after at least 12 weeks of treatment with peginterferon alfa-2a plus ribavirin will receive a low dose of peginterferon alfa-2a for 18 months. The primary objective is to evaluate safety and tolerability. Secondary objectives are to evaluate histological, virological, and biochemical effects.